Path-Q Solar
How can I separate normal electricity use from one-time unusual usage before sizing solar?
Answer
Review at least 12 months of interval or monthly bills, identify unusual events, and build a representative baseline that excludes or adjusts one-time usage. Do not simply discard an unusual month if it reflects a recurring change, such as a new appliance or electric vehicle.
Key points
- Flag construction, vacant-home periods, extreme weather, guests, temporary heating or cooling, and appliance failures.
- Compare the same months across multiple years when available.
- Separate recurring seasonal patterns from genuinely one-time events.
- Add planned future loads separately instead of hiding them in the historical average.
What it depends on
- Length and quality of the billing history
- Weather during each period
- Occupancy and behavior changes
- New or removed appliances and electric loads
- Whether interval data is available
Risks and trade-offs
- Removing a high-use month can undersize the system if the cause is now permanent.
- Sizing from the highest month can oversize the system if the event will not recur.
- A simple annual average can hide seasonal peaks that matter for bill savings or backup planning.
Information you may need
- 12 to 24 months of bills or interval data
- Dates and causes of unusual usage
- Occupancy, appliance, heating, cooling, and vehicle changes
- Planned future electricity uses
Your next step
What to do next
Mark each billing period as representative, temporary, or structurally changed, then calculate an adjusted annual and monthly baseline for design review.
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